Azobenzene-Integrated NHC Ligands: A Versatile Platform for Visible-Light-Switchable Metal Catalysis

A new class of photoswitchable NHC ligands, named azImBA,
has been
developed by integrating azobenzene into a previously unreported imidazobenzoxazol-1-ylidene
framework. These rigid photochromic carbenes enable precise control
over confinement around a metal’s coordination sphere. As a
model system, gold(I) complexes of these NHCs exhibit efficient bidirectional E–Z isomerization under visible
light, offering a versatile platform for reversibly photomodulating
the reactivity of organogold species. Comprehensive kinetic studies
of the protodeauration reaction reveal rate differences of up to 2
orders of magnitude between the E and Z isomers of the NHCs, resulting in a quasi-complete visible-light-gated
ON/OFF switchable system. Such a high level of photomodulation efficiency
is unprecedented for gold complexes, challenging the current state-of-the-art
in photoswitchable organometallics. Thorough investigations into the
ligand properties paired with structure–reactivity correlations
underscored the unique ligand’s steric features as a key factor
for reactivity. This effective photocontrol strategy was further validated
in gold(I) catalysis, enabling in situ photoswitching
of catalytic activity in the intramolecular hydroalkoxylation and
-amination of alkynes. Given the significance of these findings and
its potential as a widely applicable, easily customizable photoswitchable
ancillary ligand platform, azImBA is poised to stimulate the development
of adaptive, multifunctional metal complexes.